1. Field of the Invention
The present invention relates generally to electrical circuits and, more specifically, the present invention relates to electrical circuit trimming.
2. Background Information
In electrical circuit manufacture, it is often desirable to trim the circuit operation after the circuit is assembled in order to compensate for manufacturing tolerances. Known techniques to achieve trimming of electrical parameters at final assembly include the use of trimming potentiometers which add circuitry, are prone to instability (under mechanical/thermal stress) and also require human interaction to provide the adjustment. Other techniques include the use of wire links (jumpers) or resistors assembled onto the printed circuit board and subsequently disconnected (or clipped) to trim circuit parameters. These techniques add cost and complexity since they often require human interaction to provide the trim and add components to the electrical circuit.
Known power supplies employ sensing of the output voltage and or current of the power supply to provide a feedback signal. The feedback signal is then used by a switching regulator to accurately control the output characteristic. Typically, such power supplies employ direct output voltage and current sensing. Other configurations employ an indirect sensing of the output, often using the windings of the transformer to derive information about the output. The indirect sensing techniques are sometimes attractive as they eliminate some circuitry. However, indirect sensing techniques typically suffer from poorer voltage and current regulation accuracy since the feedback information is influenced by other factors such as transformer manufacturing tolerances, which are difficult and expensive to improve.